The purpose of the present invention is to extract iodine from liquid effluents with the object of preparing it industrially or to eliminate it from the effluents which it pollutes.
Iodine is widely disseminated in nature and its industrial preparation, in particular, poses the problem of its concentration from aqueous solutions. The same problem is posed during its recovery, for economic reasons, from liquid effluents. It is likewise important to concentrate the radioactive iodine liberated during the treatment of nuclear fuels with the object of its recovery or its elimination by storage.
Different techniques for the concentration of the iodine contained in low doses in aqueous solutions have been described.
The dissolved iodine can be absorbed by porous bodies such as activated charcoal, zeolite, alumina, magnesia, silica gel, molecular sieves, or glass powder. The absorption power of these bodies can be very high when the solutions to be extracted are highly loaded with iodine, but is insufficient in the case in which these solutions contain very low iodine concentrations. This absorption power can be improved by the impregnation of the porous bodies with a metal or a metal salt which reacts with the iodine. Iodides are then formed and the elution thereof then presents difficulties (Nouveau Traite de Chimie Minerale (New Treatise of Mineral Chemistry) by Paul Pascal, edited by Masson, volume XVI, pp. 451 to 477).
Iodine in aqueous solution can be fixed on anion exchange resins (see Chemical Abstracts vol. 74, No. 8, reference 33 067). However, this fixation is possible only if the solutions do not contain anions apt to become preferentially fixed to the iodine on these resins. The regeneration of these resins transforms the fixed iodine into metallic iodide, necessitating an oxidation in order to recover the iodine.
The instant inventor in French Pat. No. 2,411,801, has disclosed a perfected procedure making it possible to fix the iodine in aqueous solution on resins possessing ethoxy groups having a non-ionic character, without retaining the acids or anions present in the solution, by preserving the iodine in the elementary state on the resin, with the possibility of eluting it either in the elementary state or in the combined form. The iodine is thus obtained in the concentrated form. However, this requires two operations, of which one is a fixation operation and the other is an elution operation.
Iodine could be obtained in the concentrated form in a single stage from aqueous solutions by liquid-liquid extraction, if the extraction power of the iodine solvents which are immiscible with water were adequate. However, the best known iodine solvents, such as carbon tetrachloride, chloroform, carbon disulfide, benzene, kerosene and tributyl phosphate, have a low iodine extraction power and this leads, on one hand, to the handling of large quantities of solvent in order to carry out the extraction and, on the other hand, results in iodine solutions which are very dilute.